Mitchell decided rightly that the semi elliptical wing gave the best all round performance in take off, climb, turn, speed and ability to carry guns, likewise Willy went his way with more traditional you could say wings because he went with cowl mounted/engine mounted guns, even that is not true because the centerline cannon wasn't mounted to the engine but the forward bulkhead. In the end even though they went in different directions there is probably no two fighters more closely matched than the Spit and 109. Both could go head to head with each other at any altitude and they did, up to and over 30,000ft, the close escort was in response to Goring mostly, he failed to read the battle, RAF fighters ignored Luftwaffe fighters and went for the bombers, their primary target and while there is no shortage of knockers who say the .303 was a pea shooter, compared to the 20mm but it had it's problems too, they were devastating the bomber crews so Goring insisted on close escort which took away any advantage the 109 had. In saying all that it must be remembered that Fighter commands integrated air defense was the best in the world in 1940.